Renal developmental anomalies are the leading cause of kidney failure in children, but the mechanisms of normal and abnormal renal development remain to be clearly elucidated. Gene inactivation experiments have shown that mice lacking cyclooxygenase-2 (COX-2) have severe renal pathology similar to that seen in human infants exposed to NSAIDs during pregnancy. Thus, functional COX-2 is crucial for normal renal development. Our hypothesis is that time-dependent and spatially restricted expression of COX-2 regulates lineage pathways, differentiation programs, and the function of a subset of renal cells through autocrine and paracrine actions of cell specific eicosanoids. This proposal will utilize in vivo and in vitro approaches to track the lineage of COX-2 expressing cells and assess mechanisms by which COX-2 and/or its eicosanoid products regulate renal cellular function. The synergy of whole animal investigations and cell culture approaches will answer basic questions about the biology of this enzyme in the kidney and enhance our understanding of this enzyme in the complex processes of nephrogenesis. This proposal will utilize state-of-the-art homologous recombination and imaging techniques to determine the lineage and fate of COX-2 expressing cells during normal development and during the development of the dysplastic phenotype. The specific aims are to determine 1) the anatomic relationship between COX-2 deficient cells and the renal pathology seen in COX-2 deficient mice using a visible reporter of COX-2 expression and determine the effects of COX-2 deletion on lineage and function of renal cells and 2) determine the intracellular localization and trafficking of COX-2 in renal cells using a visible, functional, regulated COX-2 fusion protein to assess production and trafficking of COX-2 in response to COX-specific and cell-specific stimuli. Generation of the labeled knockout mouse will identify and track renal cells that should make COX-2 but from which the active protein has been deleted. The fusion protein will allow assessment of the intracellular activities and functions of COX-2 in renal cells. This proposal will therefore answer vital, basic, currently inaccessible, questions about the biology of COX-2, eicosanoid pathways in the kidney, and the mechanisms by which COX-2 regulates renal development.